An opposing field spell must resolve before the current one is destroyed by game mechanics. MST would prevent this from properly occurring since field spells need to remain face-up for their effects to apply.

An opposing field spell must resolve before the current one is destroyed by game mechanics. MST would prevent this from properly occurring since field spells need to remain face-up for their effects to apply.

So essentially, MST would stop your field spell from getting destroyed.

An opposing field spell must resolve before the current one is destroyed by game mechanics. MST would prevent this from properly occurring since field spells need to remain face-up for their effects to apply.

If "Mystical Space Typhoon" is chained to "Geartown", "Mystical Space Typhoon" resolves first and destroys "Geartown" at Chain Link 2. Then, "Geartown" resolves without effect as Chain Link 1. Since it still resolves, the destruction of "Geartown" is not the last thing to happen, so you miss the timing and cannot activate the effect of "Geartown".